In such apparatus the central shaft can be axially guided in the hollow drill spindle, and at least one coupling element or key can be provided for connecting the drill chuck to the drill spindle. The coupling element can be arranged in retainers (recesses or pockets) of the drill spindle and in retainers in the chuck body of the drill chuck. As a function of its setting, the coupling element, however, will allow an operating mode in which an axial play or displacement is possible for the chuck body relative to the drill spindle, and this can be eliminated by a locking mechanism having a coupling ring.
As described in the aforementioned applications the locking mechanism can include a lock or latch element, and this can be selectively brought into a recess in the contact ring, with the lock element being actuated by the respective coupling ring which can be axially displaced but which can be secured so as not to rotate. The lock element can be moved in radial direction towards the chuck axis into a respective lock retainer.
At its rim which is directed towards the control ring, the coupling ring can have teeth which can engage in matching teeth of the control ring when the coupling ring has been moved axially towards the drill end. A control ring is provided between the chuck body and the coupling ring there, and this control ring is secured to the drill spindle.
The control sleeve carries at its interior surface a snap ring which can radially project into an annular groove of the chuck body and the snap ring, accordingly, forms an abutment which limits the axial displacement for the two lateral surfaces or flanks of the annular groove which is adapted in width to the axial displacement.
The lock element can be a ball, eg. a steel ball, which can be radially displaced and guided in a recess at the contact sleeve. In the axial direction towards the drill, corresponding to the mode without axial displacement of the chuck with respect to the drill spindle, the coupling ring pushes the ball into the annular groove of the chuck body, so that it serves as a second abutment. Consequently, the ball is in positive contact at the one side of the groove, and the spring ring which is secured at the contact sleeve is in positive contact at the other side of the annular groove. Thus, the chuck body cannot be axially displaced with respect to the contact sleeve which is secured at the drill spindle.
The abutment provided by the ball provides only a single point-contact with corresponding high-area contact pressure, and the danger that deformations can occur can arise. This, in turn, can detrimentally affect the axial securement, i.e. locking and tightening, achieved by the ball between the chuck and the contact sleeve, and may lead, furthermore, to loosening of the desired connection. This may be especially disruptive, however, when only rotary drilling operations are carried out.